1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Digital printers employing an electrophotographic process have lately become widely used in the production printing field. The digital printers employing the electrophotographic process are thus required to offer higher image quality and greater reliability. The digital printers employing the electrophotographic process are particularly required to offer, for example, improved fine line reproducibility, improved character reproducibility (e.g., improved reproducibility of characters of minute sizes corresponding to 2 to 3 points), inhibition of characters from becoming broader due to the electrophotographic process, and improved color shift correction accuracy.
In order to achieve the higher image quality, the digital printer employing the electrophotographic process includes an image processor that corrects image data through image processing. The image processor performs image processing for, for example, multi-bit data having a high resolution of 1200 dots per inch (dpi) or 2400 dpi.
The digital printer employing the electrophotographic process further includes, for example, a photosensitive drum, a light source, a polygon mirror, and a scanning optical system. Specifically, the photosensitive drum has a surface that functions as a scanned surface having photosensitivity. The light source emits a laser beam. The polygon mirror deflects the laser beam from the light source. The scanning optical system guides the laser beam deflected by the polygon mirror onto the surface (scanned surface) of the photosensitive drum. The digital printer employing the electrophotographic process modulates the light beam emitted from the light source according to the image data to thereby irradiate the scanned surface with the light beam from the light source. And by scanning the scanned surface with the light beam, the digital printer employing the electrophotographic process forms an electrostatic latent image on the photosensitive drum according to the image data.
The digital printer employing the electrophotographic process having the configuration as described above includes as the light source a laser diode array (LDA), a vertical-cavity surface-emitting laser (VCSEL), or other element having a plurality of light emitting points. This enables the digital printer employing the electrophotographic process to form an electrostatic latent image having a resolution higher than image data of 1200 dpi, specifically, a 2400-dpi or 4800-dpi electrostatic latent image.
Japanese Patent Nos. 4968902 and 4640257 each disclose a technique in which, through processing performed by an image processor, outlined portions in the image are detected and outlines are extended or pixels around white-on-black inverted characters are corrected. Thereby, inverted characters are prevented from being collapsed and improved character reproducibility is achieved. Japanese Patent No. 4912071 discloses an arrangement in which a light source drive circuit includes a light source modulation signal generating circuit that corrects bend and skew in a scanning line (a locus of a light beam deflected by a polygon mirror).
Processing of a high-density image involves a problem in data transfer from the image processor to the light source drive circuit downstream thereof. If the image processor processes multi-bit data images with a resolution, for example, of 2400 dpi or 4800 dpi, the degree of freedom in image processing is enhanced and reproducibility of 1200-dpi characters and lines of minute sizes can be improved. In high-density image processing, however, an enormous amount of data needs to be transferred from the image processor to the downstream light source drive circuit, which is a bottleneck in productivity.
If the correction is made with the light source modulation signal generating circuit of the downstream light source drive circuit as in Japanese Patent No. 4912071, the amount of data transferred from the image processor to the light source drive circuit does not increase. The data transferred to the light source drive circuit is, however, converted to light source ON/OFF information, which makes it difficult to perform complicated corrections.
In view of the foregoing situation, there is a need to provide an image forming apparatus capable of performing image processing at high resolutions without increasing an image data transfer amount.